The present disclosure relates to an optical pickup control circuit and optical disc drive device for suppressing oscillation in the tilt direction at the time of reproducing an optical information recording medium.
In the optical disc drive device, the focus actuator performs tracking for surface wobbling of an optical disc, and the tracking actuator performs tracking for the eccentricity of the optical disc, and the tilt actuator corrects (adjusts) the tilt of the optical disc with respect to the optical axis.
For the focusing and the tracking, a feedback control is performed by generating an error signal from the returning light from the optical disc. In contrast, for the tilt, a feed forward control is generally performed since it is difficult to detect the tilt thereof from the returning light. Further, it is the premise that the optical axis is structurally fixed at a certain tilt by a spindle motor. From this premise, it has been considered that the feed forward control is enough for the tilt. Hence, when oscillation additionally acts on the tilt actuator, it is difficult to cancel the oscillation, and it is also difficult to optimally correct the tilt of the optical disc. Accordingly, in order for the resonance frequency f0 of the tilt actuator not to be affected by the oscillation caused by the surface wobbling and the eccentricity of the optical disc, it is necessary for the frequency f0 to be a sufficiently high frequency relative to the rotational cycle of the optical disc.
However, in recent years, there have been advances in the reduction in size and thickness of the notebook PC, in which an optical disc drive device is built. Thus, there has been demand to reduce the size and the thickness of the optical disc drive device. As the size and the thickness of the optical disc drive device have been reduced, the size and the thickness of the optical pickup device have also been reduced. As a result, the tilt actuator is restricted, and thus it is difficult to set a sufficiently high resonance frequency f0.
As described above, in the case where it is difficult to set the resonance frequency f0 of the tilt actuator to be sufficiently high, it is necessary to make the centroid of the actuator coincide with the operation point in the focusing direction or the tracking direction. In particular, in order for oscillation in the tracking direction not to have influence on the tilt direction, it is necessary to make the operation point of the tracking accurately coincide with the centroid of the actuator (refer to FIGS. 12A and 12B). Hence, strict restrictions are necessary for the precision of the actuator components and for the operations at the time of manufacture.
As shown in FIG. 12A, in the case where there is deviation between the centroid of the actuator and the tracking operation point, thrust (torque) occurs in the tilt direction centered on the centroid thereof. In contrast, as shown in FIG. 12B, in the case where the centroid of the actuator and the tracking operation point coincide with each other, there is no thrust in the tilt direction, and the actuator becomes stable.
Japanese Unexamined Patent Application Publication No. 2003-22552 discloses an optical pickup device that controls oscillation in the tilt direction. In the optical pickup device, as shown in FIG. 2, tilt magnets 14a and 14b are provided in a lens holder 10, and tilt coils for tilting an objective lens 1 are provided at the positions opposed to the corresponding tilt magnets 14a and 14b. In addition, the tilt of the objective lens 1 in the radial direction of the optical disc is controlled by the current for correction applied to the tilt coils, thereby reducing the AC tilt.